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C Sample Question

46. main( )
    {
      int a[2][3][2] = {{{2,4},{7,8},{3,4}},{{2,2},{2,3},{3,4}}};
      printf("%u %u %u %d \n",a,*a,**a,***a);
    	  printf("%u %u %u %d \n",a+1,*a+1,**a+1,***a+1);
     	 }

    Answer:

    100, 100, 100, 2
    114, 104, 102, 3

    Explanation:

    The given array is a 3-D one. It can also be viewed as a 1-D array.

    2

    4

    7

    8

    3

    4

    2

    2

    2

    3

    3

    4

    100

    102

    104

    106

    108

    110

    112

    114

    116

    118

    120

    122

    thus, for the first printf statement a, *a, **a give address of first element . since the indirection ***a gives the value. Hence, the first line of the output.

    for the second printf a+1 increases in the third dimension thus points to value at 114, *a+1 increments in second dimension thus points to 104, **a +1 increments the first dimension thus points to 102 and ***a+1 first gets the value at first location and then increments it by 1. Hence, the output.

47. main( )
    {
      int a[ ] = {10,20,30,40,50},j,*p;
      for(j=0; j<5; j++)
        {
    printf("%d" ,*a); 
    a++;
        }
        p = a;
       for(j=0; j<5; j++) 
          {
    printf("%d " ,*p); 
    p++;
          }
     }

    Answer:

    Compiler error: lvalue required.

    Explanation:

    Error is in line with statement a++. The operand must be an lvalue and may be of any of scalar type for the any operator, array name only when subscripted is an lvalue. Simply array name is a non-modifiable lvalue.

48. main( )
    {
     static int  a[ ]   = {0,1,2,3,4};
     int  *p[ ] = {a,a+1,a+2,a+3,a+4};
     int  **ptr =  p;
     ptr++;
     printf("\n %d  %d  %d", ptr-p, *ptr-a, **ptr); 
     *ptr++;
     printf("\n %d  %d  %d", ptr-p, *ptr-a, **ptr); 
     *++ptr;
     printf("\n %d  %d  %d", ptr-p, *ptr-a, **ptr); 
     ++*ptr;
    	 printf("\n %d  %d  %d", ptr-p, *ptr-a, **ptr); 
    }

    Answer:

    111
    222
    333
    344

    Explanation:

    Let us consider the array and the two pointers with some address

    a

    0

    1

    2

    3

    4

    100

    102

    104

    106

    108

    p

    100

    102

    104

    106

    108

    1000

    1002

    1004

    1006

    1008

    ptr

    1000

    2000

    After execution of the instruction ptr++ value in ptr becomes 1002, if scaling factor for integer is 2 bytes. Now ptr - p is value in ptr - starting location of array p, (1002 - 1000) / (scaling factor) = 1, *ptr - a = value at address pointed by ptr - starting value of array a, 1002 has a value 102 so the value is (102 - 100)/(scaling factor) = 1, **ptr is the value stored in the location pointed by the pointer of ptr = value pointed by value pointed by 1002 = value pointed by 102 = 1. Hence the output of the firs printf is 1, 1, 1.

    After execution of *ptr++ increments value of the value in ptr by scaling factor, so it becomes1004. Hence, the outputs for the second printf are ptr - p = 2, *ptr - a = 2, **ptr = 2.

    After execution of *++ptr increments value of the value in ptr by scaling factor, so it becomes1004. Hence, the outputs for the third printf are ptr - p = 3, *ptr - a = 3, **ptr = 3.

    After execution of ++*ptr value in ptr remains the same, the value pointed by the value is incremented by the scaling factor. So the value in array p at location 1006 changes from 106 10 108,. Hence, the outputs for the fourth printf are ptr - p = 1006 - 1000 = 3, *ptr - a = 108 - 100 = 4, **ptr = 4.

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